Field of the Invention
The present invention relates to a processing method for a plate-shaped workpiece.
Description of the Related Art
In small-sized, lightweight electronic apparatuses represented by cell phones, device chips provided with electronic circuit (device) such as IC are indispensable for the configuration. The device chips can be manufactured, for example, by a method in which a surface (front side) of a semiconductor substrate formed of silicon or the like material is sectioned into regions by a plurality of division lines called streets, the devices are formed in the regions, and then the semiconductor substrate is divided along the streets.
In recent years, a technology has been put to practical use in which wirings of the devices are insulated from each other by a low-dielectric-constant insulation film called low-k film. With the low-k film used for insulation between the wirings, it is possible to suppress the capacitance generated between the wirings to a low level and to inhibit a delay of signals even when the spacing between the wirings is reduced due to process miniaturization. This ensures that the processing performance of the device is maintained at a high level. The aforementioned low-k film is formed by stacking a plurality of layers, and its mechanical strength is low. When the semiconductor substrate is divided through cutting by a cutting blade, for example, therefore, the low-k film would be exfoliated from the semiconductor substrate. To solve this problem, a processing method has been proposed in which the semiconductor substrate is cut after the low-k film is partly removed by irradiation with a laser beam (see, for example, Japanese Patent Laid-open No. 2003-320466). In this method, first, the laser beam is applied along the streets from the front side of the semiconductor substrate to remove part of the low-k film by ablation. Thereafter, the regions deprived of the low-k film are cut by a cutting blade, whereby the semiconductor substrate can be divided while keeping low the possibility of exfoliation of the low-k film.
Meanwhile, a test element called TEG (Test Elements Group) may sometimes be disposed on the street of the semiconductor substrate. When the aforementioned processing method is applied to the division of the semiconductor substrate, a metallic pattern contained in the TEG blocks the laser beam, so that the low-k film cannot be removed suitably. Although enhancing the output of the laser beams enables adequate removal of the low-k film, the possibility of scattering of debris is raised in that case, leading to a lowered device chip quality. To divide the semiconductor substrate, a processing method using plasma etching may be employed (see, for example, Japanese Patent Laid-open Nos. 2003-197569 and 2004-172365). In the case of plasma etching applied to processing of a semiconductor substrate formed of silicon or the like material, however, the metallic pattern contained in the TEG cannot be removed suitably.